usb: bam: Remove suspend_work

u_bam and u_bam_data driver is calling usb_bam_suspend() from
work context. usb_bam_suspend() is queuing one more work i.e.
suspend_work to perform IPA handshake. Hence avoid another
context switch and directly call usb_bam_start_suspend() directly
from usb_bam_suspend().

Change-Id: I209a3eee10b43903ddc86818259723f9144f4089
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>